This invention relates to battery powered r.f. data tokens in general, and in particular to an improved battery powered r.f. data token architecture for prolonging battery life.
Data tokens are currently known and generally comprise a cardshaped device having active electronic system elements incorporated within the token structure for enabling interactive use of the device with a wide variety of data processing systems, such as credit card charging systems which enable point-of-sale purchase transactions, debit card systems, fare collection systems for public transportation, secure access facilities, and any application which requires a data token capable of interacting with a data processing system. Data tokens have two basic configurations-one using r.f. energy to provide electrical power for the electronic circuit elements incorporated into the device; and another incorporating a small D.C. source battery for supplying the required electrical power. lin the first type using r.f. power transfer, a power transfer circuit is incorporated into the device which typically has an r.f. energy receiving circuit including elements for converting energy received from an outside source in r.f. form to usable D.C. form, which is applied to the circuitry within the device. In the second type using a battery, the battery power is continuously applied to the circuit elements within the device so that they may respond to remotely generated interrogation signals. A survey of present data token technology is set forth in a publication entitled xe2x80x9cAbout Smart Cardsxe2x80x9d available from Racom Systems, Inc. The disclosure of this publication is hereby incorporated by reference.
Data tokens using an r.f. power source suffer from the disadvantage that the active circuit elements can only operate in the presence of sufficient energy. This limitation severely reduces the operating range of such data tokens and also renders such devices sensitive to varying environmental conditions which can adversely affect the transmission of r.f. energy through the atmosphere. For these reasons, data tokens containing a battery source of D.C. power are generally preferred.
Data tokens containing a battery source of D.C. power suffer from the limitation of finite power storage: since the battery is continuously coupled to the operating electrical circuit components, there is a constant drain of electrical energy from the battery. Once the energy stored in the battery is reduced to a threshold level, the circuits within the data token cease to function, and the data token is rendered useless. In the past, efforts to combat this limitation have been largely devoted to developing more efficient batteries-i.e., batteries having a greater energy storage capacity. White this approach has resulted in some improvement in performance, this extension in the useful life of the data token has introduced the disadvantages of increased weight or size of the data token or greater cost or both, all of which are undesirable. Efforts to date to provide a battery powered data token with increased operating lifetime have not met with success.
The invention comprises a data token which incorporates a low cost power switching circuit which extends the useful operating life of the token while still employing a standard D.C. power battery and without adding any significant additional weight or size to such devices.
In a broadest aspect, the invention comprises a data token with improved operational lifetime, the data token including a housing, operational circuitry incorporated in the housing and requiring D.C. power, a source of D.C. power carried by the housing, a switch circuit having a control input terminal and a pair of power transfer terminals coupled between the source and the operational circuitry, and a frequency selector circuit having an input and an output for sensing remotely generated signals and for generating an operating signal for the switch in response to sensing the remotely generated signals so that the source is electrically disconnected from the operational circuitry in the absence of the remotely generated signals and is connected to the operational circuitry when the frequency selector senses the remotely generated signals.
The source preferably comprises a small battery having electrical energy stored therein.
The frequency selector preferably comprises a crystal having a specific resonant frequency so that the crystal only generates an operating signal for the switch when remotely generated signals of matching frequency are sensed.
The switch preferably comprises an FET switch having a control terminal coupled to the output of the frequency selector and a pair of power terminals coupled between the source and the operational circuitry.
An integrator circuit is preferably coupled between the output of the frequency selector and the control terminal of the switch in order to smooth the control signals output from the frequency selector.
By limiting energy drain from battery to only those periods when operation is required by the operational circuitry-as signified by the sensing of remotely generated signals of the correct frequency the useful life of the battery, and thus the entire data token, is significantly extended.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.